WW2 German Panzer IV

Panzerkampfwagen IV mit Hydrostatischem Antrieb

German Reich (1944)
Prototype Medium Tank – 1 Built

In 1943, an alternative drive system for the Panzer IV entered development. This was the Hydrostatischem Antrieb or Hydrostatic Drive, also known as the “Thoma” drive.
It was designed and produced in the Augsburg plant of ZF Friedrichshafen, and tested on a turret-less Panzer IV Ausf.G chassis that had been badly damaged during combat operations.

Pz IV Hydro 2
Surviving Panzerkampfwagen IV mit Hydrostatischen Antrieb in the US. Note the now sloped engine deck, and the smaller rear drive wheels. Source:


The Thoma system operated in a similar way to the petrol/electric drive system produced by Porsche for his Tiger I concept vehicle that would later become the Ferdinand/Elefant. This system was a lot safer, however, as it was a petrol/hydraulic system. This gave the benefits of the Porsche system without the fire risk that plagued it so badly.
The Panzer IV chassis underwent heavy modifications to be able to mount this new drive system. The engine compartment of the tank was almost completely removed and rebuilt. The drive was placed in the rear of the tank under a large sloping engine deck. Two oil pumps were installed behind, and connected directly to the normal Maybach HL 120 TRM engine. These powered two hydraulic motors. A swash plate drive sent the power through a reduction gear into the newly added rear drive wheels, which replaced the traditional idler wheel.

The new controls added to the Panzer, note the new control “wheel” and the many new dials. Source: Spielberger Publishing

Inside the crew compartment, the old drive shafts were removed along with the large gearbox and final drive assembly at the bow end of the vehicle. The traditional steering tillers were replaced with a crescent-like wheel, similar to the one found on Tiger I. Directional movement was achieved by two control cylinders. These cylinders regulated the volume of the oil inside the pump. This governed the amount of power the drive wheels would receive. Two large 780mm adjustable toothed idlers replaced the original Panzer IV drive sprockets.
Later in 1944, the vehicle was tested with a hydraulically powered turret. Unfortunately, more information on this modification is unavailable.

The Hydrostatic Drive system outside of the vehicle. Source: Spielberger Publishing


Only one prototype of the vehicle with this drive system was built by the time the Allies were knocking on Germany’s door. In April 1945, the US 3rd Infantry Division was advancing through southern Germany and into Bavaria. They broke into Augsburg on the 27th and had the whole city secured by the 28th. With the city, they captured the Zahnradfabrik plant, and the test vehicle.

The Turretless hull of the Panzer in the Zahnradfabrik plant. Source: Spielberger Publishing

After the war, the vehicle was shipped back to the United States, where it was subjected to thorough tests by Vickers Inc. Detroit, Michigan until at least 12th April 1946, when a report stating how the drive worked was drafted:

“The powertrain consisted of two staggered-plate oils pumps that are assembled as a unit and are driven by a 12-cylinder Maybach engine. Oil is pushed by the pumps to two separate oils engines which power the drive wheels of the tracks. The oil engines are attached to the final drive housings. The engine and power aggregate are located in the rear of the vehicle, and the vehicle is moved by rear mounted drive wheels. The volume of the pumps is controlled by the driver, who thereby controls the torque of the various pressure conditions that are created by the steering and stopping of the vehicle. In the same manner, the forward and backward movement of the vehicle is achieved by directing oil flow. Pressurized oil to activate the pumps and engines and for the high-pressure connections was advanced by a geared-wheel pump that was connected to the vehicle’s engine by direct drive.”

Pz.Kpfw IV mit hydrostatischen antrieb
This Pz.Kpfw IV mit hydrostatischen antrieb was stored in the U.S. Army Center for Military History Storage Facility, Anniston, AL, USA. It was later moved to Benning. Source: Masa Narita

Unfortunately, the German test data has been lost to history. The vehicle was left in the open, exposed to the elements, at the U.S Army Ordnance Proving Grounds, Aberdeen in Maryland. In 2015 it was moved to the U.S. Army Center for Military History Storage Facility, Anniston, AL, USA, where it has the officially long-winded designation of “Tank, Medium, Full Track, Experimental Transmission, German Army, Steel, Tan, PzKpfw IV, 75mm Gun, German, 1945, World War II”.

Tanks Encyclopedia’s own rendition of the Panzer IV with Hydrostatic Drive, by Jarosław Janas.

An article by Mark Nash

Panzer IV mit Hydrostatischem Antrieb

Dimensions 5.41 x 2.88 x 2.68 m (17.7×9.4×8.8 ft)
Total weight, battle ready 25 tons
Crew 5
Armament Rheinmetall 75 mm (2.95 in) KwK 40
2-3 MG 34/MG 42 7.92 mm (0.31 in) machine-guns
Armor From 15 to 65 mm (0.59-2.56 in)
Propulsion Maybach V12 gasoline HL 120 TRM
(220 kW) 300 bhp@2500 rpm
Suspension Leaf springs
Speed on /off road 42 km/h (26 mph)
Total production 1

Links & Resources

Panzer IV und seine Varianten (Panzer IV and its Variants) Spielberger and Doyle.
Panzer Tracts No. 4, Panzerkampfwagen IV, Grosstraktor to Panzerbefehlswagen IV
Panzer Tracts No. 4-3, Panzerkampfwagen IV Ausf.H and Ausf.J, 1943 to 1945
Germans Tanks of ww2
German Tanks of ww2

By Mark Nash

Member since 2016. Specializes in weird. 120 articles & counting...

13 replies on “Panzerkampfwagen IV mit Hydrostatischem Antrieb”

Was there any advantage to the Hydrostat transmission? It seems like a waste of resources to work on such an untested transmission type when the same engineers could be working on better improvements to other tanks.
Great article as always!

It granted slightly better acceleration and allowed the vehicle to be slightly more maneuverable. Very little was gained from the concept from the time spent on it. If a was developed further, it may have been a different story.
– TE Moderator

If I’m not completely mistaken, it was partially designed by Ferdinand Porsche (don’t quote me on that), and we all know that he had a nag for designs that were innovative, but of questionable effectiveness *cough* Tiger P *cough*

He contributed yes. Apparently, this system ironed out the frequent fires of his earlier systems.
– TE Moderator

There are a few. First of all, a hydro transmission provides continuous variation as opposed to a mechanical one that has a few steps, and can provide the same transmission range for going forward or backward. It can stand much higher torque that would have been useful for Tigers trying to pull other Tigers stuck in the mud. It has far better durability since power is transmitted oil-to metal as opposed to metal-to-metal in a conventional gearbox. On the down side, it is more expensive, requires more maintenance and it’s generally less efficient. There were tanks using hydro transmissions and there are still – WW2 era M18Hellcat and the modern Type 10 from Japan.

Think about a drive system in which there are no gears or transmission persay, eliminating a point of regular break down and failure, hrdeostaatic drive is in common use today with outstanding results and reliability

i do wonder if this and the narrow turret were put together could of been pretty lethal i know it took time to turn the turret quickly in the 3 and 4 so hydraulics could of created a slightly better reaction time in combat also would it having hydrostat trasmission make it quieter ?

Highly unlikely, the reason they didnt mount it on the Pz IV was because it was too heavy, and this version does wheight about 1,4 tons more than the normal G and it doesnt even look like that it has the additional 30mm front armor (or i am just blind or they changed it to 1 80mm plate completly.) And yes it would have been faster to accelerate because the tourque can be (almost?) directly achived. but i think if it would have been further developed the likeliness of incororating the Sloped frontal armor like the Jpz 4 would be high. (Perhaps even give it a tortionbar suspention cince the angled plates where quite heavier, but that is only my guessing.)

Does it go as fast in reverse as forwards? I am not shure how exactly to understand this “In the same manner, the forward and backward movement of the vehicle is achieved by directing oil flow” So does it mean to go in reverse the oil just pumps in the other direction and therefor can achiv the same speed as forwards? And would the Hydraulic turret drive be faster or slower than the normal electric drive?

There should have been considerably more internal space for the crew without the need for the front gearbox of the conventional tank

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